1. Field of the Invention
The present invention relates to a disk device configured to record information in and/or reproduce information recorded in a disk medium such as an optical disk or a magneto-optical disk and a disk drive controlling method applied to the disk device and more particularly to a technique used in the case that a disk is rotationally driven to perform servo control.
2. Description of the Related Art
A disk recording device that records information in a disk medium such as an optical disk or a magneto-optical disk and a disk reproducing device that reproduces information recorded in the disk medium as mentioned above include servo systems. For example, each of the above mentioned devices includes an optical pickup unit configured to emit and/or receive laser light with which a signal recording surface of an optical disk is irradiated and hence a mechanism that servo-controls the optical pickup unit may be necessary. Specifically, a focusing servomechanism for a biaxial actuator of the optical pickup unit, a tracking servomechanism and a gap servomechanism for a biaxial actuator of an optical head used in a near field may be necessary.
Incidentally, in the following description, devices configured to record data in and/or reproduce data recorded in a disk-shaped recording medium such as an optical disk by rotationally driving the disk-shaped medium such as the disk recording device and the disk reproducing device of the above mentioned types will be generally referred to as disk devices.
In the case that a voice signal and an image signal recorded using the disk device are to be reproduced, the optical disk is rotated at a high speed, for example, using a spindle motor and the rotation frequency of the spindle motor is accurately controlled using a rotation frequency control circuit. Upon high-speed rotation of the spindle motor, accurate detection of a pit will be necessary even when slight positional displacement is observed in a pit array or a substrate surface is slightly deflected. Therefore, a control system of a disk device includes a servo control unit that repetitively performs highly accurate control processing on, for example, a focusing operation and a tracking operation.
The servo control unit is configured to control operations by paying attention to the fact that, in the case that input signals of almost the same waveform are repetitively input into a control system, the input signal is of the type having a repetitive waveform and by reflecting ever occurred control errors in the currently performed control every time the input signal is repetitively input.
Upon sampling a target signal, an existing servo control device samples the target signal with a sampling signal which is in synchronization with rotation of an optical disk. In general, an output signal sent from an encoder installed in a spindle motor or obtained from a clock pulse recorded in a disk is used as the sampling signal. The output signal is in the form of N (N is an integer) pulses generated for one rotation in synchronization with rotation of the spindle motor or the disk and N sampling signal are obtained by using the output signal.
Incidentally, in the case that an encoder is not mounted on a spindle motor or it is difficult to reproduce a clock pulse from a signal recorded in a disk, a pulse signal has been typically generated on a one wave-for-one disk rotation basis from a control signal of a Hall element used to control the spindle motor. Typically, a PLL (Phase-locked loop) circuit has been configured by using the one wave-for-one rotation pulse signal as a basic clock signal so as to obtain a sampling signal of N pulses for one rotation generated in synchronization with the rotation of a disk. Generation of a one-wave pulse signal for one rotation of a disk may be relatively readily realized by attaching a Hall element to a spindle motor used.
Japanese Laid-open Patent Publication No. 2006-313589 describes an example of a configuration of a disk device to which the above mentioned servo system that performs the above mentioned repetitive servo control is applied.